reference image won't show
Background images will only be displayed in:


Camera Prespective view (Numpad 0)
Any of the preset Orthographic views:

Front/Back (Numpad 1 or Ctrl Numpad 1)

Right /Left (Numpad 3 or Ctrl Numpad 3)

Top/Bottom (Numpad 7 or Ctrl Numpad 7)


To toggle between Prespective and orthogonal view use Numpad 5